Conventionally, a sheet article such as a document or a photo is usually covered with a protective film for protection because such a sheet article is readily suffered from damage. Typically, a sheet laminating apparatus is used for laminating a sheet article between two pieces of protective films in order to achieve the protective purpose. Hereinafter, the configurations of a conventional sheet laminating apparatus will be illustrated with reference to FIG. 1.
Referring to FIG. 1, a schematic cross-sectional view of a conventional sheet laminating apparatus is illustrated. The sheet laminating apparatus 10 of FIG. 1 principally comprises a heat-treating mechanism 20, a transmitting and pressing mechanism 30 and a transfer passage 40. The heat-treating mechanism 20 includes an electrically-heated plate 21 and a heater 22.
The process for laminating a sheet article (not shown) by using the sheet laminating apparatus 10 will be described as follows. First of all, the sheet article is sandwiched between an upper thermoplastic film and a lower thermoplastic film to form a sandwich structure. Then, the sandwich structure is fed into the transfer passage 40 of the sheet laminating apparatus 10 through an entrance 41. By means of the transmitting and pressing mechanism 30, the sandwich structure is continuously transported through the passage 40. During this stage, the electrically-heated plate 21 of the heat-treating mechanism 20 transforms electricity to heat energy so as to preheat the sandwich structure. The heat energy generated by the electrically-heated plate 21 is uniformly distributed over the heater 22, and radiated through an air gap between the heater 22 and the transmitting and pressing mechanism 30 so as to heat up the transmitting and pressing mechanism 30. The transmitting and pressing mechanism 30 presses against opposite sides of the sandwich structure which is transported through the transfer passage 40, and transmits the heat energy to the sandwich structure so as to soften the thermoplastic films. The heating and pressing procedure is also referred as a laminating procedure. After being transmitted and pressed by the transmitting and pressing mechanism 30, the sheet article bonds with the softened thermoplastic films to form a laminate structure. Meanwhile, the sheet article is fixed between these two pieces of thermoplastic films.
For most conventional sheet laminating apparatuses utilizing heat energy to laminate sheet articles, the problem of getting jammed is commonly found. In a case that the sheet article is adhered to the transmitting and pressing mechanism 30 during the process of transmitting and pressing the sandwich structure, or in another case that the thermoplastic films become too soft due to the elevated temperature, the possibility of getting jam in the transfer passage 40 is largely increased. If the sheet article is jammed in the transfer passage 40, the user may generally pull out the jammed sheet article by exerting a pulling force on the sheet article. If the problem of getting jammed is very serious, however, the pulling force is usually insufficient to pull out the jammed sheet article. Under this circumstance, the sheet laminating apparatus may have a breakdown.
In a case that the documents having different thickness are laminated by the sheet laminating apparatus at the same laminating speed, different working temperatures are used. As the thickness of the document is increased, the working temperature is increased. Whereas, as the thickness of the document is decreased, the working temperature is decreased. As known, the process of adjusting the working temperature of the sheet laminating apparatus is time consuming. For example, if the working temperature of the sheet laminating apparatus is increased from 100° C. to 130° C. for laminating a thicker document, a heating time period is required. At this time, the sheet laminating apparatus is capable of laminating the documents at a working temperature of 130° C. or more. On the other hand, for laminating the document at a working temperature lower than 130° C., a cooling time period is required to decrease the working temperature.
For solving the above drawbacks, a variable-speed sheet laminating apparatus was developed. The variable-speed sheet laminating apparatus is operated at a constant working temperature but at variable hot press speeds in order to laminate documents of various thicknesses. As the thickness of the document is increased, the hot press speed is increased. Whereas, as the thickness of the document is decreased, the hot press speed is decreased. Since a controller is used to adjust the rotating speeds of the motor, the conventional variable-speed sheet laminating apparatus is not cost-effective.